Electrical system for controlling at least one gate or door or similar element of the type moved electrically

ABSTRACT

An electrical system for controlling at least one gate or door or similar element of the type moved by means of at least one corresponding electric motor includes an electric network (NTWRK) consisting of two electric wires adapted to allow the distribution of direct-current power supply and digital information, a central control unit (UC) having two terminals (T 1 ,T 2 ) adapted to be connected respectively but indifferently to the two wires of the network (NTWRK) in order to transmit direct-current power supply and to transmit and receive digital information, a certain number of peripheral units (UP), each having two terminals (T 1 ,T 2 ) adapted to be connected respectively but indifferently to the two wires of the network (NTWRK) in order to receive direct-current power supply and to receive and/or transmit digital information.

FIELD OF THE INVENTION

The present invention relates to an electrical system for controlling atleast one gate or door or similar element of the type moved by means ofat least one corresponding electric motor.

BACKGROUND OF THE INVENTION

In electrical systems for controlling an entrance gate and/or a garagedoor of a dwelling, it is typical to locate the various units which makeup the system where it is necessary and connect them through electricwires.

In a dwelling, the following, for example, may be installed: a motor forone wing of the gate, a motor for the other wing of the gate, a motorfor the garage door, a radio receiver for receiving requests formovement of the gate and of the door coming from remote controltransmitters, key-operated selectors and/or command keypads foroperating the gate or the door, various safety photocell systems (eachphotocell system is composed of a receiver and a transmitter), andluminous and/or acoustic devices for signalling the movement of the gateand the door.

Until a short time ago, the number of devices installed was fairly small(four or five) and these devices, for the sake of simplicity, werelocated very close to each other, for example next to the gate.

Recently, international safety regulations, on the one hand, and therequirements of users, on the other hand, have resulted in aconsiderable increase in the number of devices installed (often ten orso or even more) and in the impossibility of locating them close to eachother; this tendency will continue in the future.

The specific sector of doors and gates for garages for commercial andindustrial premises is governed at a European level by CEN standard prEN13241.

Installed devices of this kind are electrically connected to theelectrical control system; more precisely, generally these devices areconnected directly and locally to the peripheral units of the electricalcontrol system, which units are connected directly, by means of electricwires, to the central unit of the electrical control system, the “heart”of the system.

In these systems, therefore, many electric wires are required.

Just because of the type of application, there are many such electricwires and they are often very long (various tens of meters and, in somecase, even hundreds of meters) and therefore their cost is generallyfairly high; moreover, the cost of installing them (usually underground,preferably inside protective pipes) must be taken into consideration.

Again, because of the type of application, these electric wires arepositioned outdoors, underground and sparsely (since there aresubstantially no spatial constraints), and therefore, the risk ofcutting one of them, for example when working in a garden, is quitepossible.

Moreover, the plurality of electric wires associated with differentinstalled devices results in a complex electrical system and easilygives rise, during installation, to errors in connection (both withregard to the polarity of the wires and with regard to thecorrespondence between wires and connectors) even on the part ofqualified personnel.

A solution to the abovementioned problems, which is of interest from apractical point of view, must be simple (both in terms of theconnections and in terms of apparatus), relatively inexpensive and mustnot require either specialized knowledge or particular skill on the partof the personnel responsible for installation of the system.

SUMMARY OF THE INVENTION

The object of the present invention is that of providing a solution tothe abovementioned problems which takes into account the abovementionedconsiderations.

This object is essentially achieved by the electrical control systemhaving the characteristic features described in Claim 1, Claim 2 orClaim 3.

Further advantageous aspects of the system according to the presentinvention are described in the dependent claims.

The basic idea of the present invention is that of using an electricnetwork consisting of only two electric wires for the entire system,which are adapted to distribute both direct-current power supply anddigital information, and of imposing no constraint on the connectionbetween the equipments of the system and the network of the system.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will become more apparent from the description whichfollows, considered together with the accompanying drawings, in which:

FIG. 1 shows a diagram of a fairly complicated system according to thepresent invention;

FIG. 2 shows a conceptual diagram of a system according to the presentinvention;

FIG. 3 shows a block diagram of a central unit according to the presentinvention;

FIG. 4 shows a block diagram of a peripheral unit according to thepresent invention;

FIG. 5 shows an electrical diagram of a central unit according to thepresent invention divided into three parts (FIG. 5-A, FIG. 5-B, FIG.5-C);

FIG. 6 shows an electrical diagram of a peripheral unit according to thepresent invention;

FIG. 7 shows an electrical diagram of another peripheral unit accordingto the present invention; and

FIG. 8 shows an arrangement of two photocell systems and a diagram forconnection to the respective peripheral units of the system, accordingto the present invention.

DETAILED DESCRIPTION OF THE INVENTION

With (non-limiting) reference to FIG. 2, the electrical control systemaccording to the present invention has the function of controlling atleast one gate or door or similar element (below reference will often bemade to a gate for the sake of simplicity of the description) of thetype moved by means of at least one corresponding electric motor; thesystem comprising:

a) an electric network NTWRK consisting of two electric wires adapted toallow distribution of power supply and digital information;

b) a central control unit UC having two terminals T1,T2 adapted to beconnected respectively but indifferently to the two wires of the networkNTWRK in order to transmit direct-current power supply and to transmitand receive digital information;

c) a certain number of peripheral units UP, each having two terminalsT1,T2 adapted to be connected respectively but indifferently to the twowires of the network NTWRK in order to receive direct-current powersupply and to receive and/or transmit digital information.

FIG. 2 conceptually shows N peripheral units UP indicated by UP-1, UP-2,UP-3, . . . UP-N.

The network NTWRK according to the present invention, with its twowires, may comprise branches, as can be clearly seen in the diagram ofFIG. 1. Also in the complicated diagram of FIG. 1, the electric wiresare conceptually only two in number; basically, these wires willprobably be formed by means of a series of twin-wire cable sectionswhich are suitably connected together.

As can be seen from the diagram according to FIG. 1, the wiring is verysimple, the number of wires is minimal (two both for the power supplyand for the information) and the length of the wires is minimal ifinstallation is performed properly (branches limited to the minimumnecessary).

The units are all connected together (in parallel) on the network NTWRKand without the need to take into account the polarity; it is thereforenot possible to make mistakes during connection since there are noconstraints.

The power supply may be obtained in the form of direct current directlyfrom the network NTWRK; this power supply is designed mainly for theperipheral units which make up the system and which may therefore beextremely simplified from the point of view of the power supply. Theseperipheral units may then in turn provide a power supply to the devicesto which they are connected and which may therefore be simplifiedgreatly from the point of view of the power supply.

The circuit which generates the power supply for the network NTWRK (andtherefore for the peripheral units and if necessary for the devicesconnected to the latter) is generally located inside the housing whichcontains the central unit UC.

Depending on the type of device to which a peripheral unit is connected,the latter may have the need only to receive digital information (suchas conceptually, for example, a luminous signalling device), only totransmit digital information (such as conceptually, for example, asafety device) and both to receive and transmit digital information (aswill be clarified below).

Such an electrical control system must be connected to at least threeessential devices: an electric motor for moving the gate, a device forentering requests for movement of the gate (for example a key-operatedselector, a command keypad, a remote control receiver, etc.), a safetydevice (for example, a photocell system, a sensitive edges system, a matpresence detector, a radar presence detector, etc.).

Depending on the functions performed by the central unit UC, threedesigns of the present invention are possible.

According to a first embodiment, the system comprises at least threeperipheral units, each of which have terminals adapted to be connectedrespectively but indifferently to the two wires of the network in orderto receive direct-current power supply and to receive and/or transmitdigital information; wherein one of the peripheral units is adapted tobe electrically connected to an electric motor for controlling operationthereof; wherein one of the peripheral units is adapted to beelectrically connected to a device for entering requests for movement ofthe gate or door or similar element; wherein one of the peripheral unitsis adapted to be electrically connected to a safety device for gates ordoors or similar elements.

In other words, according to this first embodiment, the three essentialdevices are connected electrically to three different peripheral units.

According to a second embodiment, the system comprises at least twoperipheral units, each having two terminals adapted to be connectedrespectively but indifferently to the two wires of the network in orderto receive direct-current power supply and to receive and/or transmitdigital information; wherein the central unit is adapted to beelectrically connected to an electric motor for controlling operationthereof and/or to a device for entering requests for movement of thegate or door or similar element and/or to a safety device for gates ordoors or similar elements; wherein a peripheral unit is adapted to beelectrically connected to an electric motor for controlling operationthereof and/or to a device for entering requests for movement of thegate or door or similar element and/or to a safety device for gates ordoors or similar elements; wherein another peripheral unit is adapted tobe electrically connected to an electric motor for controlling operationthereof and/or to a device for entering requests for movement of thegate or door or similar element and/or to a safety device for gates ordoors or similar elements.

In other words, according to this second embodiment, one of theessential devices is connected electrically directly to the centralunit, while the other two essential devices are connected electricallyto two different peripheral units.

According to a third embodiment, the system comprises at least oneperipheral unit having two terminals adapted to be connectedrespectively but indifferently to the two wires of the network in orderto receive direct-current power supply and to receive and/or transmitdigital information; wherein the central unit is adapted to beelectrically connected to an electric motor for controlling operationthereof and/or to a device for entering requests for movement of thegate or door or similar element and/or to a safety device for gates ordoors or similar elements; wherein the peripheral unit is adapted to beelectrically connected to an electric motor for controlling operationthereof and/or to a device for entering requests of movement of the gateor door or similar element and/or to a safety device for gates or doorsor similar elements.

In other words, according to this third embodiment, two of the essentialdevices are connected electrically directly to the central unit, whilethe third essential device is connected electrically to a peripheralunit.

In all three embodiments, it is possible to provide many otherperipheral units to be connected electrically to additional devices, forexample: other motors, other input devices, other safety devices,signalling devices, etc.

In all three embodiments, it is also possible to provide additionaldevices that are connected electrically directly to the central unit.

The diagram in FIG. 1 shows a system according to the present inventionwhich is fairly complicated. An area A1 of the garden where an entrygate is located contains a peripheral unit U1 for the receiver of afirst photocell system, a peripheral unit U2 for a flashing device, aperipheral unit U3 for the receiver of a second photocell system, aperipheral unit U4 for a motor operating the right-hand wing of thegate, a peripheral unit U5 for a motor actuating the left-hand wing ofthe gate, a peripheral unit U6 for the transmitter of the secondphotocell system, a peripheral unit U7 for the transmitter of the firstphotocell system, and a peripheral unit U8 for a key-operated selectorof the gate. An area A2 of the dwelling contains only the central unitUC. Finally, a peripheral unit U9 is provided for a remote controlreceiver in a point such as to receive without difficulty the remotecontrol signals. The twin-wire network NTWRK connects electrically allthese units sparsely located in an optimum manner. Obviously otherperipheral units for other devices could be connected to the networkNTWRK; this is indicated by a section in broken lines.

The basic idea of the present invention, namely that of using anelectric network consisting of only two electric wires for the entiresystem, which are adapted to allow distribution of both direct-currentpower supply and digital information, and of imposing no constraints onthe connection between the equipments of the system and the network ofthe system, requires the use of suitable circuitry inside the controlunit UC and the peripheral units UP.

With reference to FIG. 3, a possible advantageous structure of a centralunit UC which can be used in the system according to the presentinvention will be described below.

This central unit UC comprises a voltage generator circuit GT having anoutput coupled to one of the two terminals T1,T2 of the central unit (inthe example, terminal T2) and adapted to generate a direct power supplyvoltage (for example +12 volts) and a modulating circuit MOD coupledbetween this output and this terminal and adapted to modulate the directsupply voltage through digital information.

The most simple modulation to be performed in this case is ON/OFFmodulation: for example, when the central unit UC transmits a digitalvalue “1”=“high”, the difference in potential between the two wires ofthe network NTWRK will be approximately equal to +12 volts and when thecentral unit UC transmits a digital value “0”=“low”, the difference inpotential between the two wires of the network will be approximatelyequal to 0 volts.

The central unit UC may comprise further a current detector circuit RChaving an input coupled to another one of the two terminals T1,T2 of thecentral unit (in the example terminal T1) and adapted to extract digitalinformation from the current at its input; since the circuit RC willhave an influence on the potential difference between the two wires ofthe network NTWRK, the voltage drop caused by it must be small.

With reference to FIG. 4, a possible advantageous structure of aperipheral unit UP which can be used in the system according to thepresent invention will be described below.

This peripheral unit UP comprises a polarity adapter circuit AP havingtwo inputs and two outputs, the two inputs being coupled respectively tothe two terminals T1,T2 of the peripheral unit. Therefore, at theoutputs of the circuit AP there will be electric signals having apredetermined polarity irrespective of the polarity of the electricalsignals at the terminals T1,T2.

The peripheral unit UP may further comprise a power supply circuit ALhaving inputs coupled respectively to the outputs of the polarityadapter circuit AP. This circuit may be fairly simple since it isalready possible to draw from the network NTWRK a direct voltage (forexample +12 volts) with the correct polarity owing to the circuit AP. Itonly remains to eliminate, therefore, the effects of transmission by thecentral unit UC and any disturbances.

The peripheral unit UP may further comprise a voltage detection circuitRT having inputs coupled respectively to the outputs of the polarityadapter circuit AP and adapted to extract digital information from thevoltage at its inputs. If the central unit UC modulates ON/OFF thevoltage on the network NTWRK, this signal is substantially already readyto be sampled and discriminated by the peripheral unit UP. For example,if the sample has a voltage value greater than +8 volts it willcorrespond to a digital value “1”=“high” and if the sample has a voltagevalue less than +4 volts it will correspond to a digital value“0”=“low”.

The peripheral unit UP may further comprise a load circuit CC havingoutputs coupled respectively to the outputs of the polarity adaptercircuit AP and adapted to load it according to digital information. Asimple way of doing this is to adopt an ON/OFF approach in this casealso: for example, when the peripheral unit UC wishes to transmit adigital value “1”=“high”, the circuit CC applies to the network (bymeans of the circuit AP) a load which causes an additional current flowon the network NTWRK and, when the peripheral unit UC wishes to transmita digital value “0”=“low”, the circuit CC does not apply any load to thenetwork and therefore does not cause any additional current flow on thenetwork NTWRK. These differences in current are detected by the circuitRC of the central unit UC.

All the peripheral units UP are connected in parallel to the networkNTWRK and it is therefore necessary, during design of the voltagegenerator GT of the central unit UC, to take into account the currentconsumed by all the connected circuits AL, RT, CC.

According to a preferred embodiment of the present invention, thetransmission of digital information both in voltage form from thecentral unit UC to the peripheral units UP and in current form from theperipheral units UP to the central unit UC uses the PWM (Pulse WidthModulation) ⅓–⅔ approach. Each bit has a predetermined durationconsidered unitary: if the pulse lasts less than one third of thispredetermined duration, the bit has a logic value, for example, “0”,whereas if the pulse lasts more than two thirds of this predeterminedduration, the bit has a logic value, for example “1”.

For the sake of completeness of the description, some detailedelectrical diagrams of specific embodiments of parts of the systemaccording to the present invention have been appended to the presentdescription.

FIG. 5 shows the electrical diagram of a central unit according to thepresent invention divided into three parts FIG. 5-A, FIG. 5-B and FIG.5-C. FIG. 5-A shows the interface part of the central unit with thenetwork NTWRK; FIG. 5-B shows the radio section of the remote controlreceiver of the central unit; and FIG. 5-C shows the remaining part ofthe central unit.

FIG. 6 shows the electrical diagram of a peripheral unit adapted to beconnected to a receiver of a photocell system and to the network NTWRK.

FIG. 7 shows the electrical diagram of a peripheral unit adapted to beconnected to the transmitter of a photocell system and to the networkNTWRK.

Below, aspects of the present invention which are more closely linkedwith operation of the system will be described.

In order to be adapted to exchange digital information correctly andefficiently, it is advantageous for each of the peripheral units tocomprise memory means adapted to store an own unit identification codewhich may be used as an address. These memory means may consist of aconventional semiconductor memory (of the EPROM, EEPROM, FLASH or RAMtype) or, more simply, of dip switches or also, even more simply, ofjumpers. The choice depends both on cost criteria and on installationcriteria: in fact the unit identification code may be determined eitherduring production or during installation and may be fixed or variable.

In the specific examples according to FIG. 6 and FIG. 7, for example,the code is determined by one or more jumpers and by four contactsarranged in the corners of a square: if there are two jumpers, these maybe connected both horizontally, both vertically, or one horizontal andone vertical in four different ways: if there is only one jumper it maybe connected horizontally at the top, horizontally at the bottom,vertically on the right and vertically on the left.

For the safety devices consisting of a transmitting section and areceiving section (which are generally located well apart from eachother), for example photocell systems, two associated peripheral unitsmay be provided, being adapted to be connected respectively to thetransmitting section and to the receiving section and being identifiedby the same unit identification code. In this way, if the central unitneeds to transmit digital information to the photocell system (forexample a status reading request), a single transmission to the sameaddress may be effected.

A particularly effective and efficient solution for establishingcommunication between a central unit and peripheral units consists inexchanging packets of digital information using the “master-slave”technique, wherein the central unit operates as the “master” and theperipheral units operate as “slaves”. In other words, a peripheral unitwaits to be interrogated by the central unit before transmitting apacket of digital information.

Depending on the type of device connected to the peripheral unit, when aperipheral unit receives a packet from the central unit, it might not bestrictly necessary for the peripheral unit to transmit a response packetto the central unit. This typically occurs when the central unittransmits to the peripheral unit a command for activating a motor or asignalling device. For the central unit, however, it is advantageousthat a response should be transmitted in any case; in fact, for example,this response packet could contain the information that the command hasbeen carried out successfully, wherein failure to receive thisconfirmation could activate repetition of the transmission.

In the case of the “master-slave” technique, in order to ensure orderedcommunication between the central unit and peripheral units, the centralunit may advantageously be adapted to transmit packets on the network ata fixed and predetermined rate, for example one every 10 or 20 or 30 ms.

In this case it is necessary to decide to whom the packets are to beaddressed. Many criteria may be used, where on the one hand, it isnecessary for the central unit to interrogate with a certain frequencythe peripheral units connected to the input devices so as to be able torealize of any requests for opening or closing, and on the other hand,it is necessary for the central unit to control suitably (by means ofthe peripheral units) the motor and the signalling devices. Also, thecentral unit must interrogate with a certain frequency, during themovement of the motor, the peripheral units connected to the safetydevices in order to realize of dangerous situations. Below otherconsiderations which may influence the choice of destination will beclarified.

One or more of the peripheral units may be adapted to extract timinginformation from the fixed-rate transmission of packets by the centralunit. In fact, fixed-rate transmission, in addition to ensuring orderedcommunication within the system, distributes a unique timing informationwhich is valid for the whole network and on the basis of whichsynchronization may be performed, if necessary.

It is reasonable that the length of the packets which are transferredwithin the network NTWRK should be the same, in particular for thepackets transmitted from the peripheral units. The structure of thepackets transmitted from the central unit may, if necessary, differ fromthe structure of the packets transmitted from the peripheral units. Inview of the type of application, the structure of the digitalinformation packet may in any case be extremely simple: the packet fromthe central unit may consist, for example, essentially of a combinationof the code of the peripheral unit and a sequence of one or two or threebits which identify a command, while the packet from the peripheralunits may consist, for example, essentially only of short sequence ofdata bits.

In order to facilitate greatly the installation of the system, thecentral unit may be adapted to perform, during starting or re-startingof the system, identification of all the active peripheral unitsconnected to the network by means of an exchange of packets; thus thecentral unit determines autonomously the composition of the system.

In order to obtain a diagnostics procedure for the system, the centralunit may be adapted to perform, repeatedly during operation of thesystem, identification of all the active peripheral units connected tothe network by means of an exchange of packets. By comparing the list ofactive peripheral units upon start-up of the system with the list ofperipheral units which are active at a certain moment, it is possible toobtain, after any appropriate verification, identification of the faultyor isolated peripheral units. In connection with the faulty or isolatedperipheral unit, the peripheral unit may decide to take suitablemeasures (light up a lamp, stop the system, activate an alarm).

By suitably choosing the unit identification codes and the structure ofthe digital information packets (and obviously the software inserted inthe central control unit), it is possible to program the central unit bymeans of a programming device connected to a particular peripheral unitidentified by a reserved identification code.

The present invention has been described hitherto with reference toentrance gates and garage doors for homes, but it is obvious that it isapplicable and its protection therefore extends to other similar closingelements, in particular other types of gates and doors; for example,problems similar to those mentioned arise in the sector of road barriersand shutters for factories and shops.

An important aspect of an electrical system for controlling a closingelement which is moved electrically is the reliability regarding theexchange of digital information. In some cases, problems with regard toexchange could result in undesirable occurrences (for example, failureof the gate to open), but in other cases could also result in seriousaccidents (for example, a person being trapped between the wings of agate).

Errors in the exchange of information are primarily due to disturbancesin the system network which overlap with the electrical data signalsgenerated within the network itself. The errors may also be due tooverlapping of two transmission operations performed by two differentunits of the system.

In a system such as that described above, a first measure which can beadopted in order to improve the reliability of data exchange, inparticular in order to avoid errors due to overlapping, is that of usingthe “master-slave” technique (already mentioned above). In fact, theperipheral units transmit only upon a request from the central unit andthe central unit interrogates only one peripheral unit at a time.

In a system such as that described above, a second measure which may beadopted in order to improve the reliability of data exchange, inparticular in order to avoid errors due to disturbances, is that ofproviding a procedure whereby, following transmission of digitalinformation, in particular a packet. For a source to a destination, thedestination always provides a response to the source in the form ofdigital information, in particular a packet; for example, depending onthe type of destination, the response may be a simple confirmation ofreceipt (acknowledgement) or an actual item of data.

In the case where the “master-slave” technique is used, the source isalways the central unit of the system and the destination one of theperipheral units of the system.

In a system such as that described above, a third measure which may beadopted to improve the reliability of data exchange, in particular inorder to avoid errors due to disturbances, is that of providing that thesame digital information is transmitted twice from the same source tothe same destination. Typically the information could be sent insuccession, where in this case, the destination may consider thetransmission valid only if the digital information received coincides.In the case of packet transmission, the source could transmit, forexample, twice in succession the same packet to the same destination. Itis obvious that this solution results in doubling of the amount of datatraffic in the network.

It is also possible for the duplication of the transmission to beperformed on the basis of predetermined criteria. For example, a choicewhich is a good compromise in terms of reliability and traffic is thatof repeating the transmission only in relation to specific destinations;for example, the undesired illumination of a luminous signalling device(i.e. without an actual command from the system) is an event which maybe acceptable, while the undesired closing of a gate (i.e. without anactual command from the system) is an event which is not acceptableowing to the risk of injury or damage. It is therefore possible, forexample, to divide the peripheral units into “high risk” units and “lowrisk” units and duplicate only the information which is transmitted tothe “high risk” units.

In the case where the “master-slave” technique is used, it may beadvantageously provided that the only the central unit of the system,namely the “master” automatically transmits twice its digitalinformation, in particular its packets, destined for the peripheralunits, namely the “slaves”. With regard to the peripheral units, if thecentral unit, on the basis of predetermined criteria, considers that itis necessary to duplicate transmission it will duplicate interrogation.This could be the case of safety devices, the transmitted data of whichis extremely important for the central unit and for the system.

A measure which is quite widely used in order to determine errors intransmission of digital information is the parity bit. Well known in thetelecommunications sector, moreover, is the existence of fairlycomplicated codes which allow the detection and/or correction of one ormore transmission errors.

Even if the “master-slave” technique is used, it is not possible toeliminate entirely the risk that two peripheral units may transmit datato the central unit at the same time and therefore generate errors dueto overlapping of two transmission operations. This could occur, forexample, in the case where, owing to disturbances, two differentperipheral units might regard the same packet of digital information asbeing destined for them.

In a system such as that described above, a fourth measure which may beadopted to improve the reliability of data exchange, in particular inorder to detect errors due to overlapping, is that of complicating thestructure of the digital information packet: in this case, the packetcomprises a data part and a check part. It is highly unlikely that, whenreceiving digital information resulting from the overlapping of twopackets, the data part and the check part will correspond to each other.

If the “master-slave” technique is used, any overlapping generallyoccurs during response to interrogation by the “master”. It maytherefore be advantageously decided that the structure of the packettransmitted by the “master” should contain only the data(address+command) plus a parity bit and that the structure of the packettransmitted by a “slave” should contain both a data part and a checkpart without the parity bit. The check part could be provided in manydifferent ways, and a simple and effective solution will be describedbelow.

The data part and the check part of the packet are chosen with the samelength (for example 4 or 8 bits). The source which wishes to senddigital information on the network takes a data digital sequence; takesa random digital sequence with the same length as the data (continuouslygenerated in a known manner within the source); generates a digitalcheck sequence by means of an EXCLUSIVE-OR operation between the datasequence and the random sequence; and inserts into the packet the datasequence and the check sequence and transmits the packet over thenetwork. The destination receives the packet and performs the reverseoperation (which is again an EXCLUSIVE-OR operation), extracting thedigital data sequence transmitted in the absence of overlapping. Ifoverlapping has occurred with a packet transmitted by another unit, thedigital sequence extracted by the destination will not correspond to thedigital data sequence transmitted, but the destination will be unable todetect this. If the source re-transmits the digital data sequence, therandom digital sequence which is used will be different and thereforethe second packet transmitted is different. The destination receives asecond packet different from the first packet which has not beenoverlapped or been subject to different overlapping. If there has beenno overlapping during both the transmission operations, the destinationextracts the same digital sequence, but if, during at least one of thetransmission operations, there has been overlapping, the destinationobtains two different digital sequences and therefore detects the error.

Another important aspect of an electrical system for controlling aclosing element which is moved electrically is safety: it is necessaryto prevent the movement of the closing element from inadvertentlycausing damage to objects and, in particular, injury to persons.

A quite common way of obtaining this result is to identify an areainside which the movement of the closing element occurs and to stop thismovement if an object or a person enters into this area.

The safety devices most used for monitoring areas in these applicationsare photocell systems.

As is well known, a photocell system is composed of a transmitter and areceiver. If the system is correctly installed, when the system isactive, the transmitter emits light rays which are received by thereceiver; if an object or a person passes in between the transmitter andthe receiver, the light rays do not reach the receiver and thissituation is signalled by the system.

For proper monitoring of an area it is often necessary to use more thanone photocell system and a suitable arrangement along the perimeter.

FIG. 8 shows, in schematic form, a sliding gate CA located between twowalls M1 and M2, two photocell systems FC1, FC2 composed respectively oftwo transmitters FC1-T,FC2-T and two receivers FC1-R,FC2-R.

Apparently the two photocell systems monitor adequately the area wherethe gate CA moves. If a person P, for example, crosses the line whichjoins the transmitter FC2-T and the corresponding receiver FC2-R, thelight beam of the photocell system FC2 is interrupted and the gate CAstops.

In reality, the two photocell systems FC1 and FC2 may interfere witheach other; in fact, owing to the closeness of the two systems FC1 andFC2, the light rays emitted by the transmitter of one of the twophotocell systems reach the receiver of this photocell system, but alsothe receiver of the other photocell system (albeit with a reducedintensity).

In this case, and as shown in FIG. 8, there is the risk that, even ifthe person P has entered into the monitored area, the gate CA is notstopped by the electrical control system because the two receivers FC1-Rand FC2-R continue to receive light rays.

In order to solve this problem, it is possible to alternate andsynchronize operation of the two photocell systems. If we assume thatthe first photocell system FC1 is made to operate for 10 ms, followingwhich the photocell system FC2 is made to operate for 10 ms, and thatthis same procedure is continued afterwards, interference between thetwo systems is avoided.

Obviously this solution may be extended to a greater number of photocellsystems.

Synchronization between the photocell systems may be obtained by meansof a suitable circuitry connected to them.

With an electrical control system similar to that described above, it ispossible to avoid advantageously this additional circuitry, as will bedescribed below with reference to FIG. 8.

Four peripheral units UP-4, UP-5, UP-6, UP-7 of the electrical controlsystem are provided. The peripheral units UP-4, UP-5, UP-6, UP-7 areconnected respectively to the transmitter FC1-T, to the receiver FC1-R,to the transmitter FC2-T and to the receiver FC2-R. The central unit ofthe system is prepared so that it transmits over the network digitalinformation packets at a fixed rate (for example every 30 ms). The fourperipheral units UP-4, UP-5, UP-6, UP-7 are arranged so that they detectthe packets and extract from this fixed-rate transmission a clock signalwith a fixed period (30 ms in the example) which will be identical forall four units, wherein period of the clock signal may be divided intotwo equal parts. During the first part the system FC1 is activated bythe units UP-4 and UP-5 and during the second part the system FC-2 isactivated by the units UP-6 and UP-7.

A simple and advantageous manner for achieving this alternation inoperation may be the following.

Four unit identification codes are assigned to the four peripheral unitsUP-4, UP-5, UP-6, UP-7; two odd codes (which are not necessarilydifferent) are assigned to the units UP-4 and UP-5 and two even codes(which are not necessarily different) are assigned to the units UP-6 andUP-7. The units UP-4 and UP-5 will activate respectively the transmitterFC1-T and the receiver FC1-R of the system FC1 during the (odd)sub-period 1 of each period of the extracted clock signal; and the unitsUP-6 and UP-7 will activate respectively the transmitter FC2-T and thereceiver FC2-R of the system FC2 during the (even) sub-period 2 of eachperiod of the extracted clock signal.

Obviously these solutions may be extended to a greater number ofphotocell systems. Four systems should be sufficient to cover anyrequirement; in this case the alternation could be obtained by means ofthe last two bits of the unit identification code.

It must not be forgotten that the sub-period must have a duration whichis sufficiently long to allow the reliable detection of an interruptionin the light rays and that the period must have a duration which issufficiently short to comply with the requirements stipulated by theinternational standards.

1. An electrical system for controlling at least one gate or door movedby means of at least one corresponding electric motor, said electricalsystem comprising: a) an electric network consisting of two electricwires adapted to allow distribution of power supply and digitalinformation; b) a central control unit having two terminals adapted tobe connected respectively, but indifferently, to said two wires of saidnetwork in order to transmit direct-current power supply and to transmitand receive digital information; c) three or more peripheral units, eachhaving two terminals adapted to be connected respectively, butindifferently, to said two wires of said network in order to receivedirect-current power supply and to receive and/or transmit digitalinformation; wherein one of said peripheral units is adapted to beelectrically connected to an electric motor for controlling operationthereof; wherein one of said peripheral units is adapted to beelectrically connected to a device for entering requests of movement ofthe gate or door; wherein one of said peripheral units is adapted to beelectrically connected to a safety device for the gate or door; whereinthe transmission of digital information from said central control unitto said peripheral units takes place in voltage form; and wherein thetransmission of digital information from said peripheral units to saidcentral control unit takes place in current form.
 2. An electricalsystem for controlling at least one gate or door moved by means of atleast one corresponding electric motor, said electrical systemcomprising: a) an electric network consisting of two electric wiresadapted to allow distribution of power supply and digital information;b) a central control unit having two terminals adapted to be connectedrespectively, but indifferently, to said two wires of said network inorder to transmit direct-current power supply and to transmit andreceive digital information; c) two or more peripheral units, eachhaving two terminals adapted to be connected respectively, butindifferently, to said two wires of said network in order to receivedirect-current power supply and to receive and/or transmit digitalinformation; wherein said central control unit is adapted to beelectrically connected to an electric motor for controlling operationthereof and/or to a device for entering requests of movement of the gateor door and/or to a safety device for the gate or door; wherein a firstone of said peripheral units is adapted to be electrically connected toan electric motor for controlling operation thereof and/or to a devicefor entering requests of movement of the gate or door and/or to a safetydevice for the gate or door; wherein a second one of said peripheralunits is adapted to be electrically connected to an electric motor forcontrolling operation thereof and/or to a device for entering requestsof movement of the gate or door and/or to a safety device for the gateor door; wherein the transmission of digital information from saidcentral control unit to said peripheral units takes place in voltageform; and wherein the transmission of digital information from saidperipheral units to said central control unit takes place in currentform.
 3. An electrical system for controlling at least one gate or doormoved by means of at least one corresponding electric motor, saidelectrical system comprising: a) an electric network consisting of twoelectric wires adapted to allow distribution of power supply and digitalinformation; b) a central control unit having two terminals adapted tobe connected respectively, but indifferently, to said two wires of saidnetwork in order to transmit direct-current power supply and to transmitand receive digital information; c) one or more peripheral units, eachhaving two terminals adapted to be connected respectively, butindifferently, to said two wires of said network in order to receivedirect-current power supply and to receive and/or transmit digitalinformation; wherein said central control unit is adapted to beelectrically connected to an electric motor for controlling operationthereof and/or to a device for entering requests of movement of the gateor door and/or to a safety device for the gate or door; wherein one ofsaid peripheral units is adapted to be electrically connected to anelectric motor for controlling operation thereof and/or to a device forentering requests of movement of the gate or door and/or to a safetydevice for the gate or door; wherein the transmission of digitalinformation from said central control unit to said peripheral unitstakes place in voltage form; and wherein the transmission of digitalinformation from said peripheral units to said central control unittakes place in current form.
 4. The electrical system according to claim1, wherein said central control unit comprises: a voltage generatorcircuit having an output coupled to a first one of said two terminals ofsaid central control unit, and adapted to generate a direct supplyvoltage, and a modulating circuit coupled between said output and saidfirst one of said two terminals of said central control unit, andadapted to modulate the direct supply voltage through digitalinformation.
 5. The electrical system according to claim 4, wherein saidcentral control unit comprises a current detection circuit having aninput coupled to a second one of said two terminals of said centralcontrol unit, and adapted to extract digital information from thecurrent at its input.
 6. The electrical system according to claim 1,wherein each of said peripheral units comprises a polarity adaptercircuit having two inputs and two outputs, said two inputs being coupledrespectively to said two terminals of a respective one of saidperipheral units, and wherein said polarity adapter circuit permits saidperipheral units to be connected indifferently to said two electricwires.
 7. The electrical system according to claim 6, wherein each ofsaid peripheral units comprises a power supply circuit having inputscoupled respectively to the outputs of said polarity adapter circuit. 8.The electrical system according to claim 6, wherein each of saidperipheral units comprises a voltage detection circuit having inputscoupled respectively to the outputs of said polarity adapter circuit andadapted to extract digital information from the voltage at its inputs.9. The electrical system according to claim 6, wherein each of saidperipheral units comprises a load circuit having outputs coupledrespectively to the outputs of said polarity adapter circuit and adaptedto load the network according to digital information.
 10. The electricalsystem according to claim 1, wherein each of said peripheral unitscomprises a memory means adapted to store an own unit identificationcode.
 11. The electrical system according to claim 10, wherein thesafety device for the gate or door comprises a transmitting section anda receiving section, and wherein two of said peripheral units areadapted to be connected respectively to the transmitting section and tothe receiving section and are identified by the same unit identificationcode.
 12. The electrical system according to claim 1, wherein theelectrical system is adapted to establish communication between saidcentral control unit and said peripheral units through exchange ofpackets of digital information according to a “master-slave” technique,wherein said central control unit operates as “master” and saidperipheral units operate as “slaves”.
 13. The electrical systemaccording to claim 12, wherein said central control unit is adapted totransmit packets on said network at a fixed and predetermined rate. 14.The electrical system according to claim 13, wherein the destination ofthe transmission of a packet by said central control unit is one of saidperipheral units chosen on a basis of predetermined criteria.
 15. Theelectrical system according to claim 13, wherein at least one of saidperipheral units is adapted to extract timing information from thefixed-rate transmission of packets by said central control unit.
 16. Theelectrical system according to claim 12, wherein the structure of thepackets transmitted on said network by said peripheral units is fixedand comprises a data part and a check part.
 17. The electrical systemaccording to claim 16, wherein the data part and the check part have thesame length, and wherein the check part is the result of an EXCLUSIVE-ORoperation between the data part and a random digital sequence having thesame length.
 18. The electrical system according to claim 12, whereinsaid central control unit is adapted to perform, during starting andre-starting of the system, identification of all active ones of saidperipheral units connected to said network through exchange of packets.19. The electrical system according to claim 12, wherein said centralcontrol unit is adapted to perform, repeatedly during operation of thesystem, identification of all active ones of said peripheral unitsconnected to said network through exchange of packets in order toidentify faults in the system.
 20. The electrical system according toclaim 1, wherein said central control unit is adapted to transmit thesame digital information twice to the same one of said peripheral unitson the basis of predetermined criteria.
 21. The electrical systemaccording to claim 1, wherein any or each of said peripheral units isadapted to transmit digital information to said central control unitevery time it receives digital information destined for it from saidcentral control unit.
 22. The electrical system according to claim 1,wherein a first one of said peripheral units is adapted to beelectrically connected to a transmitting section of the safety device,wherein a second one of said peripheral units is adapted to beelectrically connected to a receiving section of the safety device, andwherein said first and second peripherals units are adapted to extracttiming information from a fixed-rate transmission of packets by saidcentral control unit and are further adapted to activate correspondingsections for a first time period of predetermined duration and on thebasis of the timing information.
 23. The electrical system according toclaim 22, wherein a third one of said peripheral units is adapted to beelectrically connected to a transmitting section of another safetydevice, wherein a fourth one of said peripheral units is adapted to beelectrically connected to receiving section of the other safety device,wherein said third and fourth peripheral units are adapted to extracttiming information from a fixed-rate transmission of packets by saidcentral control unit and are further adapted to activate correspondingsections for a second time period of predetermined duration and on thebasis of the timing information, and wherein the first time period andthe second time period do not overlap each other temporally.
 24. Theelectrical system according to claim 2, wherein said central controlunit comprises: a voltage generator circuit having an output coupled toa first one of said two terminals of said central control unit andadapted to generate a direct supply voltage, and a modulating circuitcoupled between said output and said first one of said two terminals ofsaid central control unit, and adapted to modulate the direct supplyvoltage through digital information.
 25. The electrical system accordingto claim 3, wherein said central control unit comprises: a voltagegenerator circuit having an output coupled to a first one of said twoterminals of said central control unit, and adapted to generate a directsupply voltage, and a modulating circuit coupled between said output andsaid first one of said two terminals of said central control unit, andadapted to modulate the direct supply voltage through digitalinformation.
 26. The electrical system according to claim 24, whereinsaid central control unit comprises a current detection circuit havingan input coupled to a second one of said two terminals of said centralcontrol unit, and adapted to extract digital information from thecurrent at its input.
 27. The electrical system according to claim 25,wherein said central control unit comprises a current detection circuithaving an input coupled to a second one of said two terminals of saidcentral control unit, and adapted to extract digital information fromthe current at its input.
 28. The electrical system according to claim2, wherein each of said peripheral units comprises a polarity adaptercircuit having two inputs and two outputs, said two inputs being coupledrespectively to said two terminals of a respective one of saidperipheral units, and wherein said polarity adapter circuit permits saidperipheral units to be connected indifferently to said two electricwires.
 29. The electrical system according to claim 3, wherein each ofsaid peripheral units comprises a polarity adapter circuit having twoinputs and two outputs, said two inputs being coupled respectively tosaid two terminals of a respective one of said peripheral units, andwherein said polarity adapter circuit permits said peripheral units tobe connected indifferently to said two electric wires.
 30. Theelectrical system according to claim 28, wherein each of said peripheralunits comprises a power supply circuit having inputs coupledrespectively to outputs of the said polarity adapter circuit.
 31. Theelectrical system according to claim 29, wherein each of said peripheralunits comprises a power supply circuit having inputs coupledrespectively to the outputs of said polarity adapter circuit.
 32. Theelectrical system according to claim 28, wherein each of said peripheralunits comprises a voltage detection circuit having inputs coupledrespectively to the outputs of said polarity adapter circuit and adaptedto extract digital information from the voltage at its inputs.
 33. Theelectrical system according to claim 29, wherein each of said peripheralunits comprises a voltage detection circuit having inputs coupledrespectively to the outputs of said polarity adapter circuit and adaptedto extract digital information from the voltage at its inputs.
 34. Theelectrical system according to claim 28, wherein each of said peripheralunits comprises a load circuit having outputs coupled respectively tothe outputs of said polarity adapter circuit and adapted to load thenetwork according to digital information.
 35. The electrical systemaccording to claim 29, wherein each of said peripheral units comprises aload circuit having outputs coupled respectively to the outputs of saidpolarity adapter circuit and adapted to load the network according todigital information.
 36. The electrical system according to claim 2,wherein each of said peripheral units comprises a memory means adaptedto store an own unit identification code.
 37. The electrical systemaccording to claim 3, wherein each of said peripheral units comprises amemory means adapted to store an own unit identification code.
 38. Theelectrical system according to claim 36, wherein the safety device forthe gate or door comprises a transmitting section and a receivingsection, and wherein two of said peripheral units are adapted to beconnected respectively to the transmitting section and to the receivingsection and are identified by the same unit identification code.
 39. Theelectrical system according to claim 37, wherein the safety device forthe gate or door comprises a transmitting section and a receivingsection, and wherein two of said peripheral units are adapted to beconnected respectively to the transmitting section and to the receivingsection and are identified by the same unit identification code.
 40. Theelectrical system according to claim 2, wherein the electrical system isadapted to establish communication between said central control unit andsaid peripheral units through exchange of packets of digital informationaccording to a “master-slave” techniques wherein said central controlunit operates as “master” and said peripheral units operate as “slaves”.41. The electrical system according to claim 3, wherein the electricalsystem is adapted to establish communication between said centralcontrol unit and said peripheral units through exchange of packets ofdigital information according to a “master-slave” technique, whereinsaid central control unit operates as “master” and said peripheral unitsoperate as “slaves”.
 42. The electrical system according to claim 40,wherein said central control unit is adapted to transmit packets on saidnetwork at a fixed and predetermined rate.
 43. The electrical systemaccording to claim 41, wherein said central control unit is adapted totransmit packets on said network at a fixed and predetermined rate. 44.The electrical system according to claim 42, wherein the destination ofthe transmission of a packet by said central control unit is one of saidperipheral units chosen on a basis of predetermined criteria.
 45. Theelectrical system according to claim 43, wherein the destination of thetransmission of a packet by said central control unit is one of saidperipheral units chosen on a basis of predetermined criteria.
 46. Theelectrical system according to claim 42, wherein at least one of saidperipheral units is adapted to extract timing information from thefixed-rate transmission of packets by said central control unit.
 47. Theelectrical system according to claim 43, wherein at least one of saidperipheral units is adapted to extract timing information from thefixed-rate transmission of packets by said central control unit.
 48. Theelectrical system according to claim 40, wherein the structure of thepackets transmitted on said network by said peripheral units is fixedand comprises a data part and a check part.
 49. The electrical systemaccording to claim 41, wherein the structure of the packets transmittedon said network by said peripheral units is fixed and comprises a datapart and a check part.
 50. The electrical system according to claim 48,wherein the data part and the check part have the same length, andwherein the check part is the result of an EXCLUSIVE-OR operationbetween the data part and a random digital sequence having the samelength.
 51. The electrical system according to claim 49, wherein thedata part and the check part have the same length, and wherein the checkpart is the result of an EXCLUSIVE-OR operation between the data partand a random digital sequence having the same length.
 52. The electricalsystem according to claim 40, wherein said central control unit isadapted to perform, during starting and re-starting of the system,identification of all active ones of said peripheral units connected tosaid network through exchange of packets.
 53. The electrical systemaccording to claim 41, wherein said central control unit is adapted toperform, during starting and re-starting of the system, identificationof all active ones of said peripheral units connected to said networkthrough exchange of packets.
 54. The electrical system according toclaim 40, wherein said central control unit is adapted to perform,repeatedly during operation of the system, identification of all activeones of said peripheral units connected to said network through exchangeof packets in order to identify faults in the system.
 55. The electricalsystem according to claim 41, wherein said central control unit isadapted to perform, repeatedly during operation of the system,identification of all active ones of said peripheral units connected tosaid network through exchange of packets in order to identify faults inthe system.
 56. The electrical system according to claim 2, wherein saidcentral control unit is adapted to transmit the same digital informationtwice to the same one of said peripheral units on the basis ofpredetermined criteria.
 57. The electrical system according to claim 3,wherein said central control unit is adapted to transmit the samedigital information twice to the same one of said peripheral units onthe basis of predetermined criteria.
 58. The electrical system accordingto claim 2, wherein any or each of said peripheral units is adapted totransmit digital information to said central control unit every time itreceives digital information destined for it from said central controlunit.
 59. The electrical system according to claim 3, wherein any oreach of said peripheral units is adapted to transmit digital informationto said central control unit every time it receives digital informationdestined for it from said central control unit.
 60. The electricalsystem according to claim 2, wherein a first one of said peripheralunits is adapted to be electrically connected to a transmitting sectionof the safety device, wherein a second one of said peripheral units isadapted to be electrically connected to a receiving section of thesafety device, and wherein said first and second peripherals units areadapted to extract timing information from a fixed-rate transmission ofpackets by said central control unit and are further adapted to activatecorresponding sections for a first time period of predetermined durationand on the basis of the timing information.
 61. The electrical systemaccording to claim 3, wherein a first one of said peripheral units isadapted to be electrically connected to a transmitting section of thesafety device, wherein a second one of said peripheral units is adaptedto be electrically connected to a receiving section of the safetydevice, and wherein said first and second peripherals units are adaptedto extract timing information from a fixed-rate transmission of packetsby said central control unit and are further adapted to activatecorresponding sections for a first time period of predetermined durationand on the basis of the timing information.
 62. The electrical systemaccording to claim 60, wherein a third one of said peripheral units isadapted to be electrically connected to a transmitting section ofanother safety device, wherein a fourth one of said peripheral units isadapted to be electrically connected to receiving section of the othersafety device, wherein said third and fourth peripheral units areadapted to extract timing information from a fixed-rate transmission ofpackets by said central control unit and are further adapted to activatecorresponding sections for a second time period of predeterminedduration and on the basis of the timing information, and wherein thefirst time period and the second time period do not overlap each othertemporally.
 63. The electrical system according to claim 61, wherein athird one of said peripheral units is adapted to be electricallyconnected to a transmitting section of another safety device, wherein afourth one of said peripheral units is adapted to be electricallyconnected to receiving section of the other safety device, wherein saidthird and fourth peripheral units are adapted to extract timinginformation from a fixed-rate transmission of packets by said centralcontrol unit and are further adapted to activate corresponding sectionsfor a second time period of predetermined duration and on the basis ofthe timing information, and wherein the first time period and the secondtime period do not overlap each other temporally.